Q
QuestionChemistry

Why is copper nitrate written as Cu(2$)2 instead of CuNO^3 when the valency of copper is + 1? Why do we use the (II) valency of copper (+ 2) only in the formula of copper nitrate?
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Step 1:
I'll solve this problem step by step, explaining the concept of valency and ionic compound formation.

Step 2:
: Understanding Valency

Valency is the combining capacity of an element. For transition metals like copper, the valency can vary. Copper can exist in two common oxidation states: + 1 (cuprous) and + 2 (cupric).

Step 3:
: Copper's Oxidation States

Cu^{2+}$$ (copper(II) ion)
- Copper can form two different ions:

Step 4:
: Nitrate Ion Composition

- The nitrate ion has a fixed composition: $$NO_{3}^{-}
- Each nitrate ion carries a - 1 charge

Step 5:
: Balancing Charges in Copper Nitrate

- For $$Cu^{2+}$$: Requires 2 nitrate ions to balance the charge
- To create a neutral compound, we need to balance the positive and negative charges

Step 6:
: Explaining the Formula

- $$Cu(NO_{3})_{2}$$ represents copper(II) nitrate
- Charge balance: Cu^{2 +} + 2(NO_{3}^{-}) = 0 - This ensures electrical neutrality

Final Answer

Copper nitrate is written as Cu(NO3)2 because the copper(II) ion (Cu^{2 +}) requires two nitrate ions (NO_{3}^{-}) to create a neutral compound. The + 2 valency is used to achieve charge balance, making the compound electrically neutral. Key Insight: The choice of copper's oxidation state depends on the specific compound and the need to balance electrical charges.